Process for electrochemical metallization of dielectrics

ABSTRACT

A solution for electrochemical metallization of dielectrics comprising a salt of copper, a phosphorus-containing salt, a stabilizing agent and water which contains, as the phosphorus-containing salt, a salt of hypophosphorous acid, the components being employed in the following proportions, g/l: 
     copper salt: 35 to 350 
     hypophosphorous acid salt: 35 to 400 
     stabilizing agent: 0.004 to 250 
     water: up to 1 liter. 
     A process for electrochemical metallization of dielectrics involving preparation of the dielectric surface, formation of a current-conducting layer thereon, electrochemical building-up of a metal coating, characterized in that the dielectric surface activation and formation of a current-conducting layer on this surface are effected simultaneously by wetting the dielectric surface with the above-specified solution, followed by a heat-treatment at a temperature within the range of from 80° to 350° C.

FIELD OF THE INVENTION

The present invention relates to the art of electrochemicalmetallization and, more particularly, to a solution and a process forelectrochemical metallization of dielectrics.

BACKGROUND OF THE INVENTION

Known in the art and extensively employed for electrochemicalmetallization of dielectrics are solutions having various compositions.Thus, use is made of solutions of surfactants for surface degreasing,i.e. imparting hydrophilic properties thereto; acid solutions of tinchloride to sensitize the surface; solutions of palladium chloride foractivation of the surface, i.e. deposition, on the dielectric surface,of metallic palladium particles which catalyze the process of chemicalcopper plating; solutions for chemical copper-plating for application,onto the dielectric surface, of a thin (1 to 3 μm) current-conductinglayer; solutions of electrolytes for electroplating build-up of a metallayer of a required thickness (cf. USSR Inventor's Certificate No.240061, published 21.03.1969, Bulletin No. 12, Cl. H 05 K 3/06).

Known in the art are also modifications of the abovementionedcombination of solutions characterized, in particular, in that for thesurface activation use is made of salts of noble metals (gold, silver,platinum and the like) and a current-conducting layer of other metals(nickel, cobalt, iron and the like) is chemically deposited onto theactivated surface. Accordingly, the solutions for chemical metallizationare also different and consist of a salt of a reducible metal (copper,nickel, cobalt, iron and the like), a reducing agent (sodium boronhydride, formaldehyde, hydrazine and the like) and a stabilizer--asolution of a complex-forming agent for the metal ions (citric acid,Seignette salt and the like), or a surface-active substance(dodecylaminacetate and the like) (cf. U.S. Pat. Nos. 3,515,649 of June2, 1970; Int. Cl. C 23f 17/00; US Cl. 204-38; 3,553,085 published Jan.5, 1971; Int. Cl. C23 d 5/60, US Cl. 204-30; 3,764,488 published Oct. 9,1973, Int. Cl. B 44 d 1/09, US Cl. 240-381.3; 3,563,784 published Oct.16, 1971, Int. Cl. C 23c 3/00, US Cl. 117-47).

Also known is a solution for electrochemical metallization ofdielectrics employed for the surface activation before a chemicalmetallization and having the following composition: PdCl₂ --0.5-1.0 g/l;H₂ SO₄ --40-200 ml/l; SnCl₂ --30-50 g/l; HCl--10-50 ml/l (U.S. Pat. No.3,650,913 published Mar. 21, 1972; Int.Cl. C 23b 50/60, US Cl. 204-30).

Also known is a combination of solutions for electrochemicalmetallization of through holes of multi-layer printed boards whichdiffers from those specified hereinbefore by the additional use of ahydrochloric-acid solution of rhodium chloride prior to the activationof the surface of the hole walls which has the following composition:rhodium chloride--4.5-5 g/l; hydrochloric acid--250-200 mg/l (cf. USSRInventor's Certificate No. 470940, published May 15, 1975, Bulletin No.18, Int.Cl. H 05K (3/00).

All the above-mentioned solutions for electrochemical metallizationcontain economically inefficient and difficult-to-obtain substances suchas salts of noble metals (palladium, gold, silver, platinum, rhodium),stabilizing agents such as citric acid and Seignette salt. Theabove-discussed prior art solutions for electrochemical metallizationhave low stability, thus necessitating frequent correction andreplacement. These solutions adapted for electrochemical metallizationdo not ensure a required quality of application of chemical coatings andan adequate reproducibility thereof.

Also known in the art is a solution for electrochemical metallization ofdielectrics which has the following composition, g/l: copper salt (ascalculated for metallic copper)--35-40; potassiumpyrophosphate--450-500; ammonia--3-6; citric acid--10-20 (cf. USSRInventor's Certificate No. 159368 published 1963. Bulletin No. 24, Cl. C23 B 5/18). This solution has but a weak activation power relative todielectrics, wherefore it does not ensure a required quality of thecurrent-conducting layer intended for electroplated building-up of ametal coating on the dielectric surface.

Known are different processes for electrochemical metallization ofdielectrics which have found an extensive use in the art.

Thus, electrochemical metallization of dielectrics is effected in thefollowing manner. The surface is degreased and washed with water. Thenthe surface is activated, prior to the deposition of thecurrent-conducting layer, by treatment thereof with a solution of tinchloride, washing, followed by treatment with a solution of palladiumchloride and washing. As a result of such activation, on the surfacethere are formed particles of metallic palladium which serve asinitiators of a chemical copper-plating process. After the latterchemical copper-plating there is effected the formation of thecurrent-conducting layer on the dielectric surface. After the subsequentwashing, the coating of the required thickness is obtained byelectroplating build-up of the metal. In this manner, the combination ofsuccessive operations constituting this process is as follows:degreasing, washing, activation, formation of a current-conducting layer(by chemical copperplating), washing, electroplating build-up of thecoating (cf. USSR Inventor's Certificate No. 240061, published Mar. 21,1969, Bulletin No. 12, Cl. H 05 K 3/06).

Another prior art process for electrochemical metallization ofdielectrics differs form the above-described in that the surfaceactivation is carried out with the use of a combined solution of tinchloride and palladium chloride which makes it possible to combineoperations of sensitization and activation into one operation and avoidone washing operation (cf. U.S. Pat. No. 3,650,913 published Mar. 21,1972, Int.Cl. C 23 B 5/60, US Class 205-30).

The above-mentioned processes for electrochemical metallization ofdielectrics are complicated due to their multistage character, longduration of the process, necessity of preparation and frequentcorrection of unstable solutions of tin chloride, combined activationsolutions, solutions of chemical metallization, necessity of utilizationof wastes of precious metals of palladium and rhodium, increasedlabour-consumption and unsatisfactory reproducibility of chemicalmetallization processes. Furthermore, these processes contemplate theuse of economically inefficient and difficult-to-obtain substances suchas salts of palladium, gold, silver, platinum, rhodium, citric acid,Seignette salt and the like.

Also known is a process for electrochemical metallization employed formetallization of walls of through holes in multi-layered printed boardswhich, in addition to the operations of the above-discussed processes,has an operation of the surface treatment in a hydrochloric-acidsolution of rhodium chloride after operations of degreasing and washing.The purpose of this operation is as follows. If metallization is carriedout by this process, then in the treatment of hole walls in the solutionof palladium chloride there occurs a contact formation of a film ofpalladium metal on end faces of copper contact plates. This palladiumfilm during manufacture and use of a printed board effectively absorbshydrogen while being transformed into palladium hydride--a brittle andnon-conducting material--which results in breaking of the mechanical andelectric contact and the board gets inoperative. The introduction of theoperation of treatment of wall of holes in a solution of rhodiumchloride makes it possible to deposit, on end faces of a copper foil, aprotective film of metallic rhodium preventing the future formation of afilm of palladium. (Cf. USSR Inventor's Certificate No. 470940 publishedMay 15, 1975, Bulletin No. 18, Int.Cl. H 05 K 3/00).

This process, likewise those described hereinabove, is multi-staged,consisting of long-duration operations necessitating correction ofunstable solutions of tin chloride, combined activation solution,solutions of chemical metallization, necessity of utilization of wastesof precious metals: palladium and rhodium. Furthermore, this processdoes not provide for a high reliability of interlayer junctions inprinted boards, since the adherence of the metallization layer with thedielectric surface of the hole wall ensures only a 3-5-time resolderingof holes.

DISCLOSURE OF THE INVENTION

The present invention is directed to the provision, by selection of anovel composition of a solution for electrochemical metallization ofdielectrics and variation of steps of the process for electrochemicalmetallization, of an activating power of the solution; to the provisionof a simplified procedure of electrochemical metallization ofdielectrics and an increased adherence of the metal layer to thedielectric surface.

This object is accomplished by that the solution for electrochemicalmetallization of dielectrics comprising a copper salt, aphosphorus-containing salt, a stabilizer and water, according to thepresent invention contains, as the phosphorus-containing salt, a salt ofhypophosphorous acid at the following proportions of the components,g/l:

copper salt: 35 to 350

salt of hypophosphorous acid: 35 to 400

stabilizer: 0,004 to 250

water: up to 1 liter.

For a more uniform crystallization of metallic copper on the dielectricsurface, this solution can additionally contain an alkali metalphosphate in an amount of from 1 to 14 g/l. Furthermore, the solutionfor electrochemical metallization of dielectrics can additionallycontain ammonium fluoride in an amount of from 2 to 36 g/l. In thepresence of this additive of ammonium fluoride the process can beeffected with the formation of a current-conducting layer on thedielectric surface at a lower temperature. The solution forelectrochemical metallization of dielectrics can also contain an alkalimetal phosphate in an amount of from 1 to 14 g/l and ammonium fluoridein an amount of from 2 to 36 g/l thus enhancing the activation power ofthe solution.

The object of the present invention is also accomplished by that in aprocess for electrochemical metallization of dielectrics involvingpreparation of the dielectric surface, activation of the dielectricsurface, creation of a current-conducting layer thereon, electrochemicalbuild-up of a metal coating, according to the present invention thedielectric surface activation and creation of a current-conducting layeron this surface are effected simultaneously by wetting the dielectricsurface with the above-mentioned solution, followed by a heat-treatmentat a temperature within the range of from 80° to 350° C. Theheat-treatment is preferably carried out by irradiation with IR-rays ata temperature of from 220° to 270° C. for 7 to 20 seconds. It isadvisable to carry out the heat-treatment also by a combined irradiationby IR- and UV-rays at a temperature within the range of from 180° to220° C. for 5 to 12 seconds.

To increase electrical conductivity of the current-conducting layerafter the heat-treatment, it is also possible to carry out a chemicalcopper-plating of the dielectric surface.

The solution for electrochemical metallization of dielectrics accordingto the present invention possesses an increased activation power.

The process according to the present invention makes it possible tosimplify the procedure of manufacture, increase adherence of the metallayer to the dielectric surface. The solution and process according tothe present invention for electrochemical metallization ensures a higherquality, as compared to the prior art solutions and processes, ofapplied, coatings, especially in electrochemical metallization ofthrough holes of printed boards, as well as in a series of applications,wherein known solutions and processes turn to be inapplicable, forexample in metallization of piezoceramics.

BEST MODE FOR CARRYING-OUT THE INVENTION

The solution according to the present invention contains ions of copper(strong oxidizing agent) and hypophosphite-ions (strong reducing agent).As copper salts use can be made of any well-soluble in water coppersalts such as copper sulphate, copper selenate, copper nitrate and thelike.

As the salts of hypophosphorous acid use can be made of such salts assodium hypophosphite, potassium hypophosphite, aluminium hypophosphiteand the like.

The quantitative proportions of the above-mentioned components of thesolution according to the present invention make it possible to ensurethe highest activation power of the solution. The solution according tothe present invention can be prepared by way of a conventionaldissolution of the components in distilled water at room temperature inthe succession specified hereinabove.

The solution contains a stabilizing agent to avoid theoxidizing-reducing interaction. As the stabilization agent for thesolution according to the present invention use can be made of suchcomplex-forming agents for copper ions as triethylenediamine,ethylenediamine, ammonia, glycerol and the like. The stabilizing effectof such complex-forming agents resides in that they hinder the transferof electrons from hypophosphite ions to copper ions. On the other hand,as the stabilizers for the solution according to the present inventionuse can be made of surfactants such as dodecylaminacetate. Suchstabilizing agents cannot hinder the direct transfer of electrons fromhypophosphite ions to ions of the reducing agent. However, this process,if it can occur, is autocatalytic in its nature, i.e. the formedparticles of metallic copper becomes centres initiating and acceleratingthis process. The stabilizing effect of similar surfactants consists inthat they passivate the copper particles originating in the solution andhinder the shifting of the reduction-oxidation to the autocatalyticprocess.

Therefore, the solution containing ions of copper and hypophosphite-ionsis rather stable at room temperature in the presence of stabilizingagents; however, it is metastable.

Upon heating of a dielectric wetted with this solution the process ofcopper reduction takes place due to activation of chemicaltransformations so that crystallization of metallic copper is developedon the dielectric surface, first of all on the surface deficiences suchas pores, crackings and the like, thus ensuring, eventually, theattained strength of adherence.

In the presence of an additive of phosphates of alkali metals (sodiumand potassium phosphates and the like) there is a more uniform fillingof the surface, while the additive of ammonium fluoride makes itpossible to carry out the process of the formation of thecurrent-conducting layer on the dielectric surface at a lowertemperature.

The process of the formation of a current-conducting layer on thedielectric surface can be carried out within a wide temperature range,the most effective is the heat-treatment under the effect ofIR-irradiation at a temperature of from 220° to 270° C. for 7 to 20seconds. The most advantageous result is attained at a combined effectof IR- and UV-radiations at a temperature within the range of from 180°to 220° C. for 5 to 12 seconds, since UV-radiation additionally promoteschemical transformations.

As a result of the heat-treatment of the dielectric surface wetted withthe above-indicated solution, a black residue of particles of afinely-divided metallic copper is formed on the dielectric surface.Because of specific properties of the finely-dispersed metal suchsurface, under the conditions of the applied electric field, becomeselectrically conductive despite the possible absence of an intimatemechanical contact of such particles. This provides for the possibilityof a direct electroplating buld-up of a metal coating of the requiredthickness while avoiding the operation of a chemical copper-plating.However, due to the same specificity of the metal properties in thestate of a high dispersity the particles of metallic copper formed atthe surface after the heat-treatment can serve as a catalyst for theprocess of a chemical copper-plating. This enables, when required, achemical copper-plating of the dielectric surface after theheat-treatment and washing in order to increase electrical conductivityof the current-conducting layer thus providing a favourable result upona further electroplating build-up of a metal layer of the requiredthickness. The formation, on the dielectric surface of acurrent-conducting layer makes it possible to ensure electrodepositionand build-up of various metals from appropriate electrolytes.

The efficiency of use of the solution and the process according to thepresent invention for electrochemical metallization can be illustratedby an example of a specific process of metallization of walls or throughholes of printed boards as the most crucial problem in the art ofmetallization of dielectrics.

The electrochemical metallization of walls of through holes in printedboards is carried out in the following manner. From a foiledglass-cloth-base laminate blanks are cut according to the board size, aphotoresist is then applied thereonto, the thus-masked plates are thenexposed, coated with the protective varnish and through holes aredrilled following the circuit pattern, the hole walls are degreased andwashed. Then the hole walls are wetted with the solution according tothe present invention, whereafter the heat-treatment is effected bypreferably IR-radiation or combination of IR- and UV-radiation until thehole walls in printed boards become black in colour and then washed.After washing, a metal layer is built-up electrochemically on the holewalls to the required thickness. This process for electrochemicalmetallization of through holes of printed boards has the followingadvantages over the prior art.

First of all, the process of electrochemical metallization of throughholes of printed boards becomes substantially simplified. Thissimplification is associated with a reduced number of process steps,lowered duration of the process (time necessary for the preparation ofthe holes for the electrochemical build-up of the coating is reducedfrom 35-40 minutes to 2-15 minutes depending on the heat-treatmentconditions), elimination of the necessity of preparation, use,correction and utilization of wastes of various solutions uponactivation of walls of the holes and chemical copper-plating thereof.The elimination of the operation of chemical copper-plating makes itpossible, in a mass-production plant, to reduce the size of theproduction line of metallization of through holes from 20 to 8 m, thussaving production floor areas and number of operating personnel.

Secondly, adherence of the metal coating to the hole walls is improved.The process according to the present invention alleviates the problemsof process reliability of adherence of the metal coating with the endfaces of copper contact plates, since the use of palladium salts isavoided. On the other hand, the process ensures an increased strength ofadherence of the metal with the dielectric surface of the hole walls.The results of tests of the adherence of a metallized piston with thehole walls have shown that holes in the boards enable a 12-15-timeresoldering, whereas boards metallized by the prior art process permitonly a 3-5-time resoldering.

Thirdly, the process according to the present invention avoids the useof economically inefficient and difficult-to-obtain substances employedin the prior art process.

For a better understanding of the present invention some specificexamples illustrating the solution and process for electrochemicalmetallization of dielectrics are given hereinbelow.

EXAMPLE 1

Use is made of a solution for electrochemical metallization ofdielectrics which has the following composition, g/l:

copper sulphate: 350

sodium hypophosphite: 400

triethylenediamine: 180.

The solution is prepared by dissolution of the components in distilledwater in the above-specified sequence. The solution is used forelectrochemical metallization of walls of through holes of printedboards for the creation of a current-conducting layer on the wallsurface prior to the electrochemical build-up.

The manufacture of printed boards is performed in the followingsequence: from a foiled glass-cloth-base laminate blanks are cut outaccording to the board size with a margine of 15 mm, a photoresist isapplied thereonto and exposed; a protective varnish is then applied andholes are made according to the circuit pattern; the hole walls aredegreased in a surfactant solution and washed. The formation of acurrent-conducting layer on the surface of the hole walls is effected inthe following manner; the blanks are wetted with the above mentionedsolution for 0.5 minute; the heat-treatment with IR-radiation iseffected for 20 seconds at the temperature of 220° C. until the walls ofthe printed board holes get black, washed in running cold water.Thereafter the protective varnish is removed; onto the hole walls andcurrent-conducting following conditions:

the composition of the electrolyte, g/l

copper sulphate: 230

sulphuric acid (specific gravity of 1.84): 60

ethanol: 10

current density: 3-4 A/dm²

time of electrochemical copper-plating is 60 minutes, the copper layerthickness is 30 μm, temperature of the solution is within the range offrom 18° to 25° C.

Thereafter, a protective silver coating is electrochemically depositedto the thickness of 12 μm, copper is etched from the spacing regions andthen the final machining of the boards is carried out.

As a result of electrochemical metallization on the surface of holewalls in printed boards there is deposited a dense, uniformfine-crystalline bright pink layer. The adherence of the metal to thesurface of the hole walls ensures the possibility of at least 12-timeresoldering of the holes which satisfies the requirements to themetallized holes of printed circuit boards.

EXAMPLE 2

Use is made of a solution for electrochemical metallization having thefollowing composition, g/l:

copper selenate: 180

sodium hypophosphite: 160

glycerol: 90

ammonium fluoride: 36.

The solution is prepared by dissolution of the components in distilledwater in the above-indicated sequence. The solution is employed forelectrochemical metallization of walls of through holes of printedcircuit boards upon the formation of a current-conducting layer on thewall surface prior to metallization by electroplating. The manufactureof a printed board is effected similarly to Example 1 hereinabove. Theformation of a current-conducting layer on the surface of the hole wallsis effected in the following manner: a blank is wetted with theabove-mentioned solution for 1 minute, then the heat-treatment withIR-radiation is carried out for 7 seconds at the temperature of 270° C.until the hole walls are black, washed in running water. Then, with theview to increase electrical conductivity of the current-conductinglayer, chemical copper-plating of the hole walls is effected in a knownsolution of the following composition, g/l:

copper sulphate: 60

sodium-potassium tartrate: 180

caustic soda: 50

sodium carbonate: 46

nickel chloride: 3

formaldehyde: 15

for 5 minutes at the temperature of 20° C.

Afterwards, the manufacture of a printed board is effected in a mannersimilar to that described in the foregoing Example 1.

As a result of electrochemical metallization, on the surface of holewalls of printed boards there is deposited a dense, uniform,fine-crystalline layer having bright-pink colour. The adherence of themetal layer to the surface of the hole walls provides for thepossibility of at least 12-time resoldering which quite satisfies therequirements to metallized holes of printed circuit boards.

EXAMPLE 3

A solution for electrochemical metallization or dielectrics has thefollowing composition, g/l:

copper sulphate: 35

potassium hypophosphite: 35

dodecylaminacetate: 0.004.

The solution is prepared by dissolution of the components in distilledwater in the above-specified succession.

The solution is employed for electrochemical metallization of both wallsof through holes and the surface of a printed board in the manufacturethereof by the semi-additive method.

The manufacture of a printed board by the semi-additive method iseffected in the following manner. A blank with drilled holes made ofglass-cloth-base laminate coated with an adhesive of epoxyrubber isdegreased by washing with dimethylformamide for 30 minutes; the adhesiveis etched for 2 minutes at the temperature of 20° C. in a solutioncontaining, g/l:

chromic anhydride: 950

sulphuric acid: 85.5

ferric sulphate: 3,

and washed with water. The formation of a current-conducting layer onthe surface of the hole walls and on the board is performed in thefollowing manner. The blank is wetted with the above-mentioned solutionfor 2 minutes and heat-treated by IR-radiation at the temperature of250° C. for 15 seconds until the hole walls and the board surface becomeblack, whereafter the blank is rinsed. In order to increase electricalconductivity of the current-conducting layer, chemical copper-plating ofthe hole walls and the board surface is effected in a known solutionhaving the following composition, g/l:

copper sulphate: 35

potassium-sodium tartrate: 60

sodium hydroxide (caustic soda): 50

sodium carbonate: 30

33% formalin: 20-30 ml/l.

The time of chemical copper-plating is 30 minutes, the temperature is20° C. The board is rinsed with water and build-up of a copper layer iseffected electrochemically on the hole walls and the board surface. Afurther manufacture of a printed circuit board is carried out byconventional techniques.

As a result of electrochemical metallization, on the surface of the holewalls and the board there is deposited a uniform, dense andfine-crystalline layer having bright pink colour. The adherence of themetal layer to the surface of the hole walls ensures the possibility ofat least 12-time resoldering which quite satisfies the requirements tometallized holes of printed boards. The adherence of the metal layerwith the board surface is 380-420 g/3 mm which is superior to theadherence attained in known processes for electrochemical metallizationof dielectrics.

EXAMPLE 4

A solution for electrochemical metallization of dielectrics has thefollowing composition, g/l:

copper nitrate: 280

potassium hypophosphite: 240

ammonia: 235

potassium phosphate: 14

ammonium fluoride: 2.

The solution is prepared by dissolution of the components in distilledwater in the above-specified succession. The solution is employed forelectrochemical metallization of piezoceramic. To this end, apiezoceramic board made of barium titanate is degreased in a surfactantsolution and rinsed. The formation of a current-conducting layer on thispiezoceramic board is effected in the following manner: the board iswetted with the above-mentioned solution for 20 seconds and subjected tothe heat-treatment at the temperature of 80° C. for 10 minutes until theboard surface becomes black, whereafter the board is rinsed with water.

Electrochemical building-up of copper onto the surface of the board iseffected in a manner similar to that described in Example 1hereinbefore.

As a result of electrochemical metallization, on the board surface thereis deposited a dense, uniform, fine-crystal layer of a bright-pinkcolour. The adherence of the metal layer to the surface of thepiezoceramic board is 400 to 430 g/3 mm.

EXAMPLE 5

A solution which is employed for electrochemical metallization ofdielectrics has the following composition, g/l:

copper selenate: 110

ammonium hypophosphite: 100

ammonia: 150.

The solution is prepared by dissolution of the components in distilledwater in the above-specified sequence. The solution is employed forelectrochemical metallization of a glass ceramic in the formation of acurrent-conducting layer on the surface thereof prior to electrochemicalbuilding-up of a metal layer. To this end, a non-ground glass ceramicboard is degreases in a surfactant solution and rinsed. Thecurrent-conducting layer on the board is created in the followingmanner: the board is wetted with the above-mentioned solution for 40seconds and then subjected to the heat-treatment at the temperature of200° C. by a combined exposure to IR- and UV-radiations for 10 secondsuntil the board surface becomes black, whereafter the board is rinsedwith water.

The electrochemical building-up of the copper layer onto the boardsurface is effected in a manner similar to that described in Example 1hereinbefore.

As a result of electrochemical metallization, on the glass ceramic boardsurface there is formed a dense, uniform, fine-crystalline layer havingbright-pink colour. The adherence of the metal layer to the surface ofthe glass ceramic board is 460-480 g/3 mm.

EXAMPLE 6

A solution which is employed for electrochemical metallization ofdielectric has the following composition, g/l:

copper sulphate: 50

potassium hypophosphite: 50

ethylenediamine: 34

dodecylaminacetate: 0.007

potassium phosphate: 14.

The solution is prepared by dissolution of the components in distilledwater in the above-specified succession. The solution is employed forelectrochemical metallization of cardboard in the formation of acurrent-conducting layer on the surface thereof prior to theelectrochemical building-up of a metal layer. To this end, a cardboardplate is degreased in a surfactant solution and rinsed. The formation ofthe current-conducting layer on its surface is effected in the followingmanner: the plate is wetted with the abovementioned solution for 30seconds and then subjected to a combined heat-treatment with IR- andUV-radiations at the temperature of 350° C. for 5 seconds until theplate surface becomes black, and then the plate is rinsed with water.

The electrochemical building-up of the metal layer on the plate surfaceis effected in a manner similar to that described in Example 1.

As a result of electrochemical metallization, on the cardboard surface adense, uniform, fine-crystalline layer is deposited which has abright-pink colour. The adherence of the metal layer to the surface ofthe cardboard plate is 350 to 370 g/3 mm.

EXAMPLE 7

A solution which is employed for electrochemical metallization ofdielectrics has the following composition, g/l:

copper nitrate: 200

sodium hypophosphite: 190

ethylenediamine: 84

sodium phosphate: 1.

The solution is prepared by dissolution of the components in distilledwater in the above-specified succession. The solution is employed forelectrochemical metallization of an ebonite article in the formation ofa current-conducting layer on the surface thereof prior toelectrochemical building-up of a metal layer. To this end, an eboniteplate is subjected to sand-blasting to impart roughness to its surface,degreased in a solution of a surfactant and rinsed. The formation of acurrent-conducting layer on the plate surface is effected in thefollowing manner: the plate surface is wetted with the above-mentionedsolution for 1 minute, followed by heat-treatment with IR- andUV-radiation together at the temperature of 220° C. for 12 seconds untilthe plate surface becomes black, whereafter the plate is rinsed withwater.

The electrochemical building-up of the metal layer onto the eboniteplate surface is effected in a manner similar to that described inExample 1 hereinbefore.

As a result of electrochemical metallization, on the surface of theebonite plate there is deposited a bright-pink layer. The adherence ofthe metal layer to the ebonite plate surface is 520-540 g/3 mm.

INDUSTRIAL APPLICABILITY

The solution for electrochemical metallization of dielectrics accordingto the present invention can be used mainly for the formation of acurrent-conducting layer on the dielectric surface prior to thesubsequent electrochemical deposition of both functional and decorativemetal coatings onto the surface of glass-cloth-base laminates, glass,ceramics, active coals, plastic powders, paper, fabric and various otherdielectrics. The solution and process for electrochemical metallizationof dielectrics according to the present invention finds an extensive usein the electrical engineering, household appliances, ship-building,aviation, car manufacture, instrument engineering and other industries;in particular, they can be used in metallization of through holes inone-side, two-side and multi-layered printed circuit boards.

We claim:
 1. A process for producing a conductive layer on a dielectricconsisting essentially of:(a) wetting at least a portion of the surfaceof the dielectric with a solution comprising:

    ______________________________________                                                         grams/liter                                                  ______________________________________                                        copper salt        50-350                                                     hypophosphorous acid salt                                                                        50-350                                                     stabilizing agent  0.004-250                                                  water              up to 1 liter                                              ______________________________________                                    

(b) heat-treating at least the portion of the surface of the dielectricwetted with the solution at a temperature in the range of 80° to 350° C.to evaporate the water and decompose the solution whereby a conductivelayer is formed.
 2. A process of claim 1 wherein the heat-treating iscarried out by irradiation with IR radiation.
 3. A process of claim 2wherein the conductivity of the conductive layer is increased byelectroplating.
 4. A process of claim 2 wherein the heat-treatment is ata temperature of from 220°-270° C.
 5. A process of claim 4 wherein theheat-treating is done for a period of from 7 to 20 seconds.
 6. A processof claim 4 wherein the conductivity of the conductive layer is increasedby electroplating.
 7. A process of claim 1 wherein the heat-treating iscarried out by irradiation with IR and UV radiation.
 8. A process ofclaim 7 wherein the conductivity of the conductive layer is increased byelectroplating.
 9. A process of claim 7 wherein the heat-treatment is ata temperature of from 180° to 220° C.
 10. A process of claim 9 whereinthe heat-treatment is carried out for 5 to 12 seconds.
 11. A process ofclaim 9 wherein the conductivity of the conductive layer is increased byelectroplating.
 12. A process of claim 1 wherein the heat-treating isdone for a period of less than about 10 minutes.
 13. A process of claim1 wherein the conductivity of the conductive layer is increased byelectroplating.